Figure 2 shows an alternating current generator.

Insulated wire pins DC supply switch 6.0 V dc X

Soft iron core

North

Reduce the dc power supply to reduce current

a) (i) Name the phenomenon used to produced an e.m.f in the coil. ………...

(ii) What is the effect on the current produced if the magnets are moved further apart from each other? Give a reason.

………. ………. b) Figure 3 shows the graph of the output current against time.

i. State the value of the peak current.

………. ii. Calculate the frequency of the alternating current.

………..

iii. On the same axes, sketch the graph output current against time if the coil is now rotated at twice the speed.

c) What are the changes that need to be made to convert this generator to a direct current motor?

……… ………

Electromagnetic induction

Current decreases. The magnetic flux becomes weaker. A lower rate of change of magnetic flux results a smaller induced current

2 A

f = 1 / 0.08 = 12.5 Hz

Replace the slip rings commutator to a commutator. Add in a direct current power supply

Current, I/A 0.04 0.08 2 -2 4 -4 Time, t/s

3. Figure shows a magnet which is pushed towards a solenoid.

a) State the magnetic poles of the two ends, P and Q of the solenoid when the magnet is moved towards the solenoid, stationary inside the solenoid and then move away from the solenoid.

………

………

b) State the Lenz’s Law ………

………

c) Suggest three ways to make the deflection angle of the Galvanometer to become bigger. ……….……….

……….………..

……….………..

d) Name four essential parts of an a.c generator ……… ……….. ………. ……….. Q P Galvanometer

Move toward  P is North pole and Q is South pole, Stationary  no pole for P and Q Move away  P is South pole and Q is North pole

Lenz’s Law states that the direction of the induced e.m.f is such that its magnetic effects

always oppose the change producing.

The relative motion between magnet and coil is increased The number of turns on coil is increased

The cross-sectional area of the coil is increased

Magnet Coils of wire Slip-rings Carbon brushes

Part C: Essay Questions

1. The transmission of electrical energy from a power station to factories and houses is by means of a system called National Grid Network.

a) State the transformation of energy in a hydroelectric power station.

b) Explain what is meant by National Grid Network and state three advantages of its distribution of electrical energy.

c) Figure 4 below shows a model for transmission of electrical power using source of 12 V a.c.

You are supposed to set up the model by using the information in the table below:

Number of turns of coils Types of transformers Material of transmission cables

1200 Solid copper core Constantan

600 Laminated soft-iron core Copper

60 Laminated copper core Nichrome

40 Wooden core Tungsten

i. Choose the number of turns of primary and secondary coil for step-up transformer. Give a reason.

ii. Choose the type of core of the step-up and step-down transformer. Give a reason. iii. Choose the type of material of transmission cables. Give a reason.

d) If the resistance of the transmission cable in the model is 20 , calculate i. the current that flows through the transmission cable

ii. the power loss due to heating effect of the transmission cable 12 V a.c

source 240 V 240 V 12 V

12 V bulb is bright Transmission wire

2. Diagrams show wire coils connected to the ammeters, switches and d.c power supply

When the switch is on and iron filings of the same amount is spread on each of the cardboard surface, the pattern of the iron fillings is formed as shown in the diagrams.

a) What is meant by magnetic field?

b) Using diagrams above, compare the number of turn of the coils, the pattern of the iron fillings and the angle of deflection of the ammeter indicator.

1.

a) Gravitational potential energy  kinetic energy  electrical energy

b) -National Grid Network is a network of underground cables and pylons cover the whole country.

-It enables the transmission of electricity to be distributed to various regions continuously.

-If any breakdown, the electric can be supply from another areas from another pylons

-It has good electrical energy consumption such as transferring the energy from low needed energy to high needed electrical energy

c)

i. 60:1200 because 60:1200 = 12:240

ii. Laminated soft-iron core because its easy to magnetized and demagnetized

iii. Copper because it has smaller resistance and can reduce the power loss d)

i. V=IR, I = 12 A ii. P = I2R

c) State the relationship between the strength of the magnetic field and i. the pattern of iron fillings

ii. the number of turn of the coils

d) Diagram shows two thin copper strips, PQ and RS, connected via circuit. Explain what happens to PQ and RS, when the switch is on.

P

Q

Q

S +

+ _ _

2 (a) Magnetic field : magnetic force region

(b) - The number of turns of the coil in Diagram 10.2 is more // vice versa

- The arrangement patterns of the iron fillings in Diagram 10.1 is further apart // vice versa.

- The angle of deflection Diagram 10.2 is bigger.

(c) (i) - The closer the pattern og iron filling , the greater strength of magnetic field / vice versa

(d) - When current flows, the magnetic field is formed // Diagram

- The direction of the current in the thin copper : The flow of current is in the opposite direction // Diagram

- The direction of magnetic field between two thin copper strips : same direction The two pieces of thin copper repulse against one another / diagram.

3. A student used the apparatus shown in figure below to investigate electromagnetic induction. The magnet will be drop inside the coil. He observed that the angle that the pointer of the

galvanometer deflects become increase when he increase the number of turns on the solenoid.

a) From the above observation, make a suitable inference b) State one appropriate hypothesis that could be investigated

c) Design an experiment to investigate the hypothesis that you stated in (b). In your description, state clearly the following:

i. Aim of experiment

ii. Variables in the experiment iii. List of the apparatus

iv. Arrangement of the apparatus

v. Procedures of the experiment on controlling the manipulated and responding variables

vi. Tabulation of the result vii. Analysis of the result

viii. State one precaution in the experiment

3.

e) Inference: The e.m.f induced in the solenoid influenced by the number of turns in the solenoid.

f) Hypothesis: The e.m.f induced in a solenoid increases when the number of turn on the solenoid increases

g)

i. Aim: To investigate the relationship between the e.m.f. induced in a solenoid and the number of turns of the solenoid

ii. Manipulated variable: Number of turns of the solenoid

Responding Variable: e.m.f induced in the solenoid // Galvanometer reading

Fixed Variable: The strength of the magnet used // the speed of magnet movement into the solenoid

iii. Magnet bar, Galvanometer, copper wire iv. See above picture

v.

1. Wind 50 turns of copper wire to make a solenoid, then connect to a galvanometer

2. Release a strong magnet bar from the top into the solenoid and take the reading of galvanometer

3. repeat the experiment using 100, 150, 200 and 250 turns of copper wire

vi. Table of result

Number of turns, N Galvanometer reading, V /divisions 50 100 150 200 250

vii. Analysis of results

Galvanometer reading, V/div

Number of turns / N